Producing aluminum fluoride-alkali-metal fluoride double compounds practically free from iron



\ Patented Aug. 4, 1925.

UNITED STATES PATENT OFFICE.

HEINRICH srnoxnrnrt, or GmEsHEIM-oiv-THE-Miim, JULIUS s'oLL, or SCHWANHEIM-ON-THE-MAIN, AND ROBERT BILFINGER, or GRIESHEIM-ON-THE-MAIN, oneMANY, ASSIGNORS T CHEMISCHE FABRIK GRIESHEIM -ELEKTRON, or FRANK-FORT-ON-THE-MAIN, GERMANY.

PRODUCING ALUMINUM FLUORIDE ALKALI-METAL FLUORIDE DOUBLE COMPOUNDSPRACTICALLY FREE FROM IRON. I

No Drawing. Original application filed September 1, 1923, Serial No,660,636. Divided and this appli- 4 cation filed Ju1y 14, 1924. SerialNo. 726,056.

To all whom it may concern:

Be it known that we, IIniNnioii Srnoxrr Tnn, acitizen of Germany, andresiding at Griesheim-on-the-Main, JULIUS SoLL, a citi- 5 Zen ofGermany, and residing at 'Schwanheim-on-the-Main, and ROBERT BILFINGER,

a citizen of Germany, and residing at Griesheim-on-the-Main, Germany,have invented certain new and useful Improvements in Producing AluminumFuoride-Alkali- Metal Fluoride Double Compounds Practically Free fromIron,.of which the following is a specification.

This invention relates to the production of aluminum-alkali-metalfluorides of the chiolite or cryolite type or of mixtures thereof whichmay be used in the manufacture of aluminum or aluminum salts in asimilar manner as pure cryolite as described in our copendingapplication Serial No. 660,636, filed September 1, 1923, from which thisapplication has been divided out.

\Ve have found that aluminum-alkalimetal double salts of high purenessand especially practically free from iron are obtained from aluminumsalts from the products resultingfrom the extraction of argil or pottersearth with mineral acid) b treating the acidfaluminous solutions a terhaving filtered off the silicious residue with an alkali-metal salt andhydrofluoric acid or with mineral acids and alkali metal fluorides undersuch conditions that the iron salt present is not precipitated to getherwith the said aluminum-alkali-metal salts. 1

One method of precipitating the alumina whilst keeping the iron salt insolution con sists in adding less hydrofluoric compounds 40 thanarerequired for the formation of aluminum-alkali-metal fluoride doublecompounds according to the reaction formula, that is -to say at the mostequivalent quancities of fluorine ions are 'to be added.

Another method of keeping the iron salt' in solution has been found toconsist in reducing to ferrous compounds the dissolved ferric salts, forinstance by means of sulphuretted hydrogen, In this case hydrofiuoriccompounds may be added to any (especially amount without contaminatingwith iron the products obtained.

As to the addition of alkali-metal salts there is no restriction. Analkali-metal salt of the acid which has served for extracting thealuminous ore may be used or an alkalimetal salt of another acid. By theaction of the hydrofluoric acid the mineral acid is recovered in thefiltrate, as far as it was combined with the aluminum and alkalimetalprecipitated or added in excess, and

this mineral acid either mixed or uniform may be used without furthertreatment for extracting new quantities of potters earth. In order toavoid more mineral acid being formed by the action of the hydrofluoricacid than is required for the extraction of the aluminous orealkali-meta1 fluoride may be wholly or partially substituted foralkali-metal chloride or sulfate.

'In order to obtainthe theoretical output of fluorine compounds it isadvisable to employ an excess also of the alkali-metal salts,

this excess not being lost, but being contained in the filtrate whichmay be used for extracting fresh quantities of potters earth, so thatthe excess of added alkali-metal salts will not be lost.

After repeated use of the filtrate for extracting new quantities ofpotters earth the The mixture is heated and stirred for half an hour.Then a hot solution of 110 kilograms of commercial sodium chloride in350 litres of water is added and the heating is still continued forabout 15 minutes to complete the precipitation of the aluminouscompounds. The well filtered precipitate is sucked oil in the heatedstate and washed out. It forms an aluminum-sodium fluoride ,grams of A10, and 16.0 per-litre inthe form of sul which is practically free fromiron.

The process may be modified in that the solution of common salt is firstadded to the aluminum salt solution and then 'theprecipitation withhydrofluoric acid is effected. In this case care must be taken foreflicacicus stirring during the addition of the. hydrofluoric acid inorder to avoid any local excess of hydrofluoric acid in the reactingmixture as the iron saltwould not be-inert against such an excess andwould be pre-.

cipitated. Y

I I Example 2.

90 kilograms of sodium chloride dissolved in 250 litres of Waten areadded to 200 litres Example 3.

:500 kilograms of a 20 percent hydrofluoric acid solution are added to500 litres of a solution containing the equivalent of 90.6 grams of Fe otion is heated to boiling and a hot solution of 170 kilograms 'of,.common salt in 500 litres of water is added. The precipitate of doublecompounds after washing and p extracting.

drying contains onlytraces of iron. The filtrate forms a mixture ofhydrochloric and sulphuric acid which may again be used for If it isdesired to avoid such mixturesthe ferric compounds may be reduced to theferrous form and then the practically pure aluminum double fluoridesprecipitated by sodium sulfate according to the following.

J Ewample 4.

y In 200 litres of a solution containing the .equivalent of'90.6 gramsof A1 0 and 16.0 grams of Fe O per litre in the form of sulfates theferric iron isreduced. to; ferrous iron by means of sulphurettedhydrogen. Then during stirring and heatinga hot solution .of 80kilograms of sodium sulfate in 200 litres of water and 250 litres ofa 20percent hydrofluoric acid are added. After sucking off. andwashing thedouble compound produced will contain only traces of the product is prac.

ates. The solu- 4 The sequence of the additions of alkali.- metalsulfate" and hydrofluoric acid may be exchanged without the result beingaffected.

However it may be desirable in some cases to operate inversely withhydrochloric or sulfuric acid and alkali-metalfluorides instead ofhydrofluoric acid and alkali-metal chloride or sulfate; this isespecially the case when sodium fluoride is to be obtained in someprocess fromgdoublefluorides (if the latter are employed).

7 Example 5. I

150 litres of concentrated hydrochloric acid areadded to 200 litres of ahydrochloric acid extract from potters earth containing the equivalentof 102.9 grams of A1 0 and 9.3 grams -Fe O "per litre. The solution is.boiled and 120 kilograms of potassium fluoride aresuccessively--intr0duced. After short stirring the precipitate ofpotassium aluminum fluoride is sucked oflz'.

Example 6.

200 litres of 1n the foregoing example are heated to degrees centigrade,anda solution of kilograms of sodium fluoride in 150 litres ofconcentrated hydrochloric acid is slowly introduced under stirring. Thestirring is" continued for a short time and the precipitate is suckedofl. The operations are susceptible of various other. changes andmodifications without departing from the spirit of the invention.Such-Jor instance, the hydrofluoric compounds may be slowly added, themixture digested for a while, and finally the alkalimetal salts may beadded. Or one half of the hydrofluoric compounds may be added,

the mixturemay be digested for a while, and finall the rest of thehydrofluoric compoun s and the alkali-metal salts may be added.

We claim I 1. Process for producing aluminum-alkali-metal doublefluorides practically free from iron, consisting in making aluminumsaltsolutions containing iron in its ferrous form-, and precipitating understirring and in presence of mineral acid the said double r fluorides bythe addition of substances which on dissolving in water form fiuorineandalkali-metal-ions.

-2. Process for producing aluminum-alkali-metal double fluoridespractically free from iron consisting in making aluminum salt solutionscontaining iron in the ferric form, .reducing the said iron to itsferrous form,'.and precipitating under stirring and in presence ofmineral acid the said double fluorides by the addition ofsubstanceswhich on *dissolving in water. form fluorineandalkali-metal-ions.

3. Process for producing aluminum-,alkait hydrochloric acid extract as Ili metal double fluorides practically free from iron consisting inmaking aluminum chloride solutions containing iron in the ferric form,reducing the said iron to its ferrous form, and precipitating understirring and in presence of mineral acidthe said double fluorides by theaddition of substances which on dissolving in water form fluorineandalkali-metal-ions.

4. Process for producing aluminum alkali-metal double fluoridespractically free from iron consisting in making aluminum salt solutionscontaining iron: in the ferric form, reducing the said iron to itsferrous form,'slowly adding under stirring and in presence of mineralacid, hydrofluoric acid digesting the mixture for a while, and finallyadding under continued stirring alkali-metal salts to precipitate thesaid double fluorides.

5. Process for producing aluminum alkafrom iron consisting in makingaluminum salt solutions containing iron in the ferric form, reducing thesaid iron to its ferrous form, slowly adding under stirring and inpresence of mineral acid only half of the hydrofluoric compoundsrequired, digesting the mixture for a while and finally adding the restof the hydrofluoric compounds and the alkali-metal salts to complete theprecipitation. t t

In testimony whereof we aflix our signatures in presence of twowitnesses.

O. C. S. B. Wms, JANE SAUSTE.

